When you sleep, you sweat out and breathe out some water, but how much is normal to lose, assuming you're not actively trying to make yourself sweat?
This is much easier to measure than to calculate.
After urinating and before going to bed, weigh yourself. After getting up, urinating and having a bowel movement (bm is mostly water) weigh yourself in the same clothes. The difference in weight is mainly due to water loss (urine loss, sweating and insensible perspiration); this will be likely ~0.5 kg or more, mostly depending on how much you sweat.
The amount of water lost by breathing is about the same as the amount of metabolic water produced in your body in the same time (NAP.edu).